One technology modifying the quality of silver halide grains and improving the total performance of a silver halide photographic light-sensitive material to a desired extent is a doping technology, i.e., a technology of incorporating a dopant which is a substance other than silver ion and a halide ion. In particular, a large number of researches on a doping technology of transition metal complex ions have been made. It is generally recognized that incorporation of a transition metal complex ion as a dopant effectively changes a photographic performance even when the amount is extremely small.
It is generally known that doping of an iridium compound having halogens as main ligands is effective for improving reciprocity failure of a silver halide emulsion. For example, JP-B-43-4935 (The term “JP-B” as used herein means an “examined Japanese patent publication”) discloses that addition of an iridium compound at the preparation of silver halide grains decreases the variation of gradation within a wide range of exposure time. Further, U.S. Pat. No. 4,997,751 describes addition of iridium from the surface of silver halide grains improves reciprocity failure.
In a silver halide emulsion having a high silver chloride content which contains an iridium compound well known as a compound improving reciprocity failure as a dopant, however, the occurrence of latensification during 15 seconds to about 2 hours after exposure is disclosed in Journal of Photographic Science, vol. 33, p. 201 by H. Zwicky. When such phenomenon occurs, sensitivity and gradation varies during exposure to development, and thus it is undesirable from a practical standpoint.
JP-A-1-105940 (The term “JP-A” as used herein means an “unexamined published Japanese patent application”) discloses that an emulsion excellent in reciprocity failure can be obtained by an emulsion of a high silver chloride content having silver bromide-rich domains to which iridium is selectively doped. However, latent image stability sometimes deteriorates when the reaction conditions for forming the silver bromide-rich domains is varied, and therefore further improvement has been desired.
With regard to the iridium compounds, iridium compounds having various ligands such as aqua, cyano, nitrosyl, and thionitrosyl are disclosed in JP-A-1-285941, JP-A-3-118535, JP-A-4-213449, JP-A-4-278940, JP-A-5-66511, JP-A-5-313277, JP-A-6-82947, JP-A-7-72569, JP-A-7-72576, JP-A-11-202440, JP-A-11-295841. In these publications, however, it is not known that the doping of an iridium aqua complex or an iridium oxo complex improves reciprocity failure without deteriorating latent image stability during several hours after exposure. As described above, there is no satisfactory technology for obtaining an emulsion excellent in reciprocity failure without deteriorating latent image stability during several hours after exposure using a silver halide emulsion of a high silver chloride content.
It is known that the doping of a compound other than iridium is also effective. U.S. Pat. No. 4,847,191 discloses silver halide grains formed in the presence of a rhodium(III) complex having 3, 4, 5 or 6 cyanide ions as ligands. This patent publication shows the reduction of the high (illumination) intensity reciprocity failure by the action of the dopant. European Patent Nos. 0336425 and 0336426, and JP-A-2-20854 each discloses a silver halide emulsion whose grains are formed by doping a rhenium, ruthenium, osmium or iridium complex having 4 or more cyano ligands. These publications describe increase in the storage stability of sensitivity and gradation and improvement in the low (illumination) intensity reciprocity failure. European Patent No. 0336427 and JP-A-2-20852 each discloses a silver halide emulsion wherein a six-cordinate vanadium, chromium, manganese, iron, ruthenium, osmium, rhenium, or iridium complex containing a nitrosyl or thionitorsyl ligand is used, whereby improvement in the low (illumination) intensity reciprocity failure is resulted in without lowering sensitivity at medium illumination intensity.